The present invention relates to data storage systems, and more particularly, this invention relates to reading located data using tape drives.
In magnetic storage systems, magnetic transducers read data from and write data onto magnetic recording media. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
Accessing data previously written to a magnetic tape typically involves locating the magnetic tape on which the data was written, retrieving the magnetic tape, loading the magnetic tape into a tape drive, aligning a magnetic head in the tape drive with the particular portion of the magnetic tape where the data is written, and actually reading the data. Attempts to reduce data access times have introduced the use of caching in combination with magnetic tape. As data is written to and/or read from magnetic tape, data is temporarily stored in a cache such that it is more easily and quickly accessible. However, as the amount of available space in the cache decreases during use, the data stored in the cache is flushed, thereby freeing the cache to store other data. Accordingly, when writing a particular file that has a size which is larger than the size of the cache, only a portion of the file remains in the cache at any point in time, thereby causing the file to be allocated to memory in discontinuous regions.